The use of fossil fuel as the combustible fuel in gas turbine engines results in the combustion products of carbon monoxide, carbon dioxide, water vapor, smoke and particulates, unburned hydrocarbons, nitrogen oxides and sulfur oxides. Of these above products, carbon dioxide and water vapor are considered normal and unobjectionable. In most applications, governmental imposed regulation are further restricting the amount of pollutants being emitted in the exhaust gases.
In the past, the majority of the products of combustion have been controlled by design modifications. For example, at the present time smoke has normally been controlled by design modifications in the combustor, particulates are normally controlled by traps and filters, and sulfur oxides are normally controlled by the selection of fuels being low in total sulfur. This leaves carbon monoxide, unburned hydrocarbons and nitrogen oxides as the emissions of primary concern in the exhaust gases being emitted from the gas turbine engine.
Oxides of nitrogen are produced in two ways in conventional combustion systems. For example, oxides of nitrogen are formed at high temperatures within the combustion zone by the direct combination of atmospheric nitrogen and oxygen and by the presence of organic nitrogen in the fuel. The rates with which nitrogen oxides form depend upon the flame temperature and, consequently, a small reduction in flame temperature can result in a large reduction in the nitrogen oxides.
Past and some present systems providing means for reducing the maximum temperature in the combustion zone of a gas turbine combustor have included water injection. An injector nozzle used with a water injection system is disclosed in U.S. Pat. No. 4,600,151 issued on Jul. 15, 1986, to Jerome R. Bradley. The injector nozzle disclosed includes an annular shroud means operatively associated with a plurality of sleeve means, one inside the other in spaced apart relation. The sleeve means form a liquid fuel-receiving chamber and a water or auxiliary fuel-receiving chamber positioned inside the liquid fuel-receiving chamber. The fuel-receiving chamber is used to discharge water or auxiliary fuel, or in addition, an alternatively to the liquid fuel. The sleeve means further forms an inner air-receiving chamber for receiving and directing compressor discharged air into the fuel spray cone and/or water or auxiliary fuel to mix therewith.
Another fuel injector is disclosed in U.S. Pat. No. 4,327,547 issued May 4, 1982, to Eric Hughes et al. The fuel injector includes means for water injection to reduce NOx emissions, an outer annular gas fuel duct with a venturi section with air purge holes to prevent liquid fuel entering the gas duct. Further included is an inner annular liquid fuel duct having inlets for water and liquid fuel. The inner annular duct terminates in a nozzle, and a central flow passage through which compressed air also flows, terminating in a main diffuser having an inner secondary diffuser. The surfaces of both diffusers are arranged so that their surfaces are washed by the compressed air to reduce or prevent the accretion of carbon to the injector, the diffusers in effect forming a hollow pintle.
The above system and nozzles used therewith are examples of attempts to reduce the emissions of oxides of nitrogen. The nozzles described above fail to efficiently mix the gaseous fluids and or the liquid fluids to control the emissions of oxides of nitrogen emitted from the combustor.